Hydraulic lash adjuster



Jan. 26, 1954 W. J. PURCHAS, JR, ET AL HYDRAULIC LASH ADJUSTER Filed Jan. 25, 1949 Gttomegs Patented Jan. 26, 1954 HYDRAULIC LASH ADJUSTER William. J. Purchas, Jr. and Robert O. Moser, Grand Rapids, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application January 25, 1949, Serial No. 72,642

8 Claims.

The present invention relates to internal combustion engines and more particularly to hydraulic tappets for automatically taking up lash or play in internal combustion engine valve operating mechanisms.

Valve operating mechanisms of internal combustion engines generally comprise a valve train of several engaging parts which transfer motion from an eccentric cam to a poppet valve. As the operating clearances between the engaging parts of the train vary to a considerable extent because of temperature variations and wear it is difiicult to effect a stable, silent and efficient operation of the engine. Accordingly, it is desirable to provide means in the train for compensating for,

such conditions.

Hydraulic tappets are particularly effective devices for automatically adjusting the clearance in such valve trains. However, the cost of manufacture and assembly has heretofore limited the Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize our invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawing in which Figure l is a longitudinal sectional view of a fragmentary portion of an internal combustion engine provided with hydraulic tappets embodying the present invention; Figure 2 is an enlarged longitudinal sectional view of one form of the tappet; Figure 3 is a view taken along the line 33 of Figure 2 and Figure 4 is an enlarged sectional view of a modified form of tappet embodying the present invention.

Referring now to the drawing and particularly to Figure 1, there is illustrated a hydraulic tappet l embodying the present invention in the valve train or operating gear of a typical internal combustion engine. In Figure 1, a cam l2 which is one of several spaced along the camshaft of the engine supplies the motion for moving the poppet valve M to its open position against the pressure of a spring [5 which in turn provides the force for returning the valve to its seat when permitted by the cam motion. As shown, the motion of the cam is transmitted to the stem of the poppet valve through a rocker arm I 8 mounted on the rocker arm shaft 20, a push rod 22 and the hydraulic tappet it] which automatically compensates for any clearance that may develop in the valve train due to wear and temperature variations. The tappet is guided for reciprocating movement in a cylindrical opening 24 in the engine block 26. Oil is supplied to the tappet from the hollow rocker arm shaft which forms a part of the pressure lubricating system, not shown. Communication between the tappet and the lubricating system is established through the passages 28 in the rocker arm shalt, passages 3a, 32 and 34 in the rocker arm and passage 35 in the push rod thereby insuring an adequate supply of oil for operating the tappet and lubricating the working parts of the tappet mechanism. To provide oil for lubricating the cooperating surfaces of the tappet and cylinder block excess oil is drained from the passage Si in the push rod and falls by gravity along the push rod surface to the tappet. Oil is supplied to the modified form of tappet illustrated in Figure 4 by a passage 38 provided in the engine block and communicating with the pressure lubricating system.

As illustrated in Figure 2 of the drawing the tappet [0 comprises a generally cylindrical member 40 having one end closed and a piston 52 reciprocably mounted within the cylindrical member to form an internal pressure chamber 44. The chamber 44 is supplied with oil from the lubricating system to provide a liquid column upon which the piston is supported and through which motion applied to the cylindrical member by the cam is transmitted to the valve train and poppet valve. The manner in which the liquid column is supplied from the lubricating system to automatically compensate for any lash or clearance that may develop in the valve train will be described in detail hereinafter in connection with the description of the piston and the operation of the tappet.

The piston 42 is formed with a cavity 36 which is in communication with the internal chamber i l through a passage 49 controlled by a one-way ball valve 50. The cavity 46 serves as a reservoir for supplying oil to the internal chamber and preferably should be of sufficient size or capacity to insure proper operation of the tappet mechanism for periods when the supply of oil from the lubricating system may be temporarily stopped. Such periods may occur during the starting of a cold engine when the oil is most viscous and therefore does not flow readily until a substantial pressure is built up in the lubricating system or they may occur when the supply of oil to the tappets of a thoroughly heated engine may be temporarily restricted or cut off. During such periods the cavity 46 will continue to supply oil to the internal chamber 44 for a substantial period of time thereby insuring efficient operation of the tappet as long as oil remains in the cavity 46. A groove 52 in the external wall of the piston substantially midway of the piston ends and connected to the cavity by a passage 54 provides a means for collecting and returning to the cavity 46, oil which has been forced upwardly along the engaging walls of the piston and cylindrical member by the pressure developed in the internal chamber when opposing forces are applied respectively to the piston and cylindrical member. The groove 52 and passage '54 thus serve to establish an oil recirculating system for the tappet mechanism within the tappet itself and provide for the return to the cavity of substantially all of the oil forced out of the internal chamber 44.

The lower portion of the piston 42 is shown terminating in a reduced end 56 which is adapted to position a ball retaining cage 58 on the end of the piston. The ball retaining cage is provided with an annular flange 60 which engages the bottom of the piston adjacent the reduced end and ports 82 oppositely disposed of the axis of the cage which permit passage of oil from the cavity 48 through passage 48 past the ball valve 50 to the internal chamber 44. The cage 58 is held in position on the reduced end by the pressure of a cylindrical spring 64 which is bottomed on the end wall of the cylindrical member and has its other end engaging the flange 60 of the valve cage 58.

To maintain the efficiency of operation that is considered desirable in a hydraulic tappet the depth of the ball retaining cage and the diameter of the ball is predetermined to provide a clearance of not less than .005" and not more than .012 between the ball 50 and the ball valve seat 66. For optimum operating conditions it is preferred that the clearance be maintained within the range of .005 to .008" inclusive. Where the clearance is under .005 there is a delay in time for transferring oil from the cavity 46 to the internal chamber 44 when the oil is very viscous and flows slowly due to low temperatures. This creates lash in the valve train and consequently introduces considerable noise from its operation. Where the clearance is greater than .012" the time required to return the ball to its seat is such that oil is pushed back through the passage 48 into cavity 46 thereby introducing lash and noise into the valve train when the oil is extremely fluid or thin due to the high operating temperatures of the engine. With a valve clearance such as described, a controlled lash is provided in the tappet itself which absorbs undesirable secondary motions imparted to the tappet cylinder by an uneven cam surface on the base circle or to the tappet by any other source of secondary deflections in the engine.

To insure that the ball will be substantially centered in the cage the passage 48 is formed with a large enough diameter which, along with the predetermined depth of the cage, permits the recessing of a portion of the ball in the passage thereby enabling the valve seat to serve additionally as a guide ring to center the ball in the cage.

In order to maintain the valve clearance substantially constant within the preferred clearance limits the valve cage is positioned on the reduced end with sufiicient clearance between the side wall of the reduced end and the side wall of the cage to permit relatively easy rotation of the cage on the piston thereby causing wear between the engaging surfaces of the annular flange and piston which compensates for any corresponding wear on the valve seat due to the valving action of the ball. To obtain cage rotation the tappet and cam surfaces are formed to supply a turning movement to the tappet thereby causing it to rotate and this action is transmitted directly to the valve cage through the spring 64 which has its ends in gripping engagement with the end wall of the cylindrical member and the annular flange 60 of the cage. To reduce wear on the engaging surface of the annular flange of the cage to a minimum the cage is formed of steel and is hardened by heat treatment. Likewise, to minimize wear on the valve seat caused by the valving action of the ball the seat is superficially hardened by heat treatment. In connection with the valve seat it has been found that particles carried by the oil frequently become lodged between the valve seat and the ball introducing severe local stresses in the material adjacent the valve seat when the ball is seated in response to the operating pressure in the interior chamber 44. Where the seat has been hardened and is not supported by suiflcient material such local stresses frequently cause fractures which interfere with the efficient operation of the valving mechanism. To prevent this condition the valve seat, in addition to being surface hardened, is formed with a radius of curvature which is preferably not less than .007" and not more than .010". With the valve seat formed in this manner there is sufficient material adjacent the seat to provide a tough wear resistant seat on which particles in the oil may collect and be crushed by the action of the ball without damaging the surface.

As maintenance of the valve clearance within the heretofore described limits is particularly desirable for optimum tappet operation any contact between the valve cage and the cylindrical member which would cause a distortion of the cage and a variation in the valve clearance should be eliminated. This is accomplished in the tappet of the present invention by providing a shoulder 68 in the internal wall of the cylindrical member at a height above the end wall substantially greater than the overall length of the valve cage. Further to prevent any contact between the cage and the cylindrical member the external diameter of the annular flange 60 is substantially less than the diameter of the internal wall of the cylindrical member immediately below the shoulder 68. The internal wall diameter of the cylindrical member is further reduced adjacent the end wall to centrally position the spring 64 for more convenient assembly of the tappet parts.

Under temperature conditions to which the tappets are exposed in an engine operating condition hard films of residue resembling solidified varnish form on areas of the piston and cylinder walls which are not in surface engagement with each other. Where the piston varies only slightly from its normal operating position, as shown, to take up lash or clearance in the valve train such hard films do not interfere with the operation of the tappet. However, where the piston undergoes considerable change of position as, for example, when the engine is not running and the tappet rests on the eccentric portion of the cam, the pressure of spring l6 forces the piston into abutting relation with shoulder 68, the hard films become wedged between the walls of the piston and cylinder causing a binding or freezing of the parts which render the tappet inoperative. This undesirable condition is substantially overcome where such films are more apt to occur by forming a groove it in the wall of the cylindrical member adjacent the shoulder 63 and in overlapping relationship with the piston wall adjacent its lower end. As the tappet normally operates in the position shown, the formation of such a film on the piston adjacent the groove would not normally interfere to bind the piston and cylinder because any movement of the piston would be downwardly in the cylinder moving the film with it away from the engaging surfaces of the piston and cylinder. Likewise, if film formations in the area of the groove 5'2 make it desirable to prevent the effects of this condition a groove similar to groove It could be formed in the internal cylinder wall adjacent and slightly above the groove 52 with the extremities of the groove above the corresponding extremities of groove 52 in its normal operating position.

The piston cavity 46 is closed at the top by a cap 12 formed with a semi-spherical recess 14 which engages the ball end of the push rod 22. A passage 76 in the cap provides communication between the passage 36 in the push rod and cavity 43 in the piston to supply the tappet with oil from the lubricating system.

The tappet ii] is assembled as a unit by inserting the spring 6:? and subsequently the piston and valve assembly. The parts are maintained in assembled relationship by the split ring 18 which snaps into a corresponding groove Bil in the wall of the cylindrical body 49. The split ring is provided with diametrically opposed straight portions 32, shown in Figure 3, which permits the use of a cap '12 having a diameter such that its peripheral edge will not engage the wall of the cylindrical member to cause wear in the wall.

Referring now to Figure 4 there is illustrated a modification of the tappet of the present invention particularly adapted to receive oil through the side walls of the piston 82 and cylindrical member 8%. The tappet is substantially the same in details of construction and operation as the tappet of Figures 1 and 2 except that the cylindrical member 84 is provided with a groove 86 in registry with the passage 38 throughout the entire operating stroke of the tappet. A passage 88 provides communication between groove 85 and the interior of the cylindrical member and is in registry with a groove 93 in the piston wall similar to groove 86. A passage 92 provides communication between groove 90 and cavity 94 of the piston 82. An additional groove 35 serving as an oil sealing groove is provided in the wall of the cylindrical member immediately above groove 85. The structure of this modification difiers further in that the piston cavity 94 is closed at the top by an elongated member 9! adapted to directly engage the valve stem. The valve cage $8 is provided with a generally conical shaped side wall to allow for a larger spring diameter and still maintain proper clearance between ball valve and cage.

In both tappet constructions the cylindrical member is made of steel or cast iron which may be heat treated or chilled respectively to provide a hard wear surface on the end of the cylindrical member to resist wear caused by the rubbing action of the cam on the end of the cylindrical member.

In operation with the tappet I0 resting on the base circle of the cam 12 oil under pressure is introduced to the piston cavity through the communicating passages connecting the tappet to the lubricating system. The oil is then forced into the internal chamber of the tappet through passage 48 and past ball valve 50 by the action of spring 64 in forcing the piston upwardly to take up any lash or clearance in the valve train. As the cam rotates and the action of the eccentric portion is transmitted to the tappet, the tappet is forced upwardly against the pressure of spring It. A pressure is built up in the internal chamber -44 which forces the ball against the valve seat 65 thereby providing a column of oil between the piston and cylindrical member which transmits the motion of the cam to the valve. With the relatively high pressure in the internal chamber some oil is forced upwardly along the engaging walls of the piston and cylindrical member where it is collected in groove 52 (Figs. 1 and 3) or (Fig. i) and returned to the piston cavity through the passage connecting the groove with the cavity. As the cam continues to rotate, the direction of the tappet changes following the face of the cam. On the return stroke the pressure of spring it continues to supply sulficient force to the piston to maintain a sealed or closed condition of the ball valve until the tappet is again riding the cam base circle. Any clearance that may have developed in the valve train during the complete cycle of valve operation is automatically compensated by the action of spring 6 in forcing the piston upwardly to take up the clearance. With this action the ball valve opens and the oil is again introduced into the interior chamber to fill the chamber for the next complete cycle of valve operation.

Along with the reciprocating movement imparted to the tappet it by cam 12 and spring It a definite and controlled rotary force is imparted to the cylindrical member by the cam. This rotary force is utilized in the tappet of the present invention to maintain a clearance between the ball valve and the valve seat desirable for the most efiicient operation of the tappet. To effect a rotary movement of the cylindrical member its cam engaging surface is formed with a spherical curvature and the cooperating surface of the cam is formed with a tapered or conical surface. In assembling the tappet in the engine it is arranged with respect to the cam so that the cam and cylindrical member engage at a point slightly oiiset from the central axis of the tappet. With this arrangement a definite and controlled rotary force is imparted to the cylindrical member by the action of the cam and it in turn is transmitted through the gripping action of spring 64 to the valve cage. As hereinbefore described, this rotary movement of the valve cage effects a wear of the engaging surfaces between valve cage and piston which compensates for the corresponding wearing action of bhB bail on the valve seat of the piston. In this manner the clearance between the ball and valve seat is effectively maintained within the limits most desirable for effective operation of the tappet.

The tappet of the present invention is particularly adapted to operate quietly at maximum efficiency over long periods of time without attention and its simplicity of construction makes it particularly adaptable to quantity production and assembly and the attendant manufacturing cost savings.

While the embodiments of the present invention as herein disclosed constitute preferred forms it is to be understood that other forms 7 might be adopted all c ming i hin the scope of the claims which follow.

What I claim as new and desire to obtain by Letters Patent of the United States 1, In a hydraulic tappet a cylinder provided with a closed end, a piston mounted for reciprocation in said cylinder, said piston having a central cavity formed therein and a passage providing communication between said cavity and the internal chamber formed by the assembled piston and cylinder, a free valve for controlling the inner end of said passage, a valve positioning cage mounted on the inner end of said piston for rotary movement relative thereto, said cage and piston having cooperating abutment surfaces axially disposed from said end of the piston, said cage accommodating a predetermined displacement of the valve between open and closed positions, a spring positioned for engagement of its ends with said cage and said closed end to transmit rotary movement from said cylinder to said cage and means in the wall of said cylinder for limiting the travel of said piston to prevent engagement of said cage with said cylinder.

2. In a hydraulic tappet, a cylinder provided with a closed end, a piston mounted for reciprocation in said cylinder, said piston having a central cavity therein and a passage providing communication between said cavity and the internal chamber formed by mounting said piston in said cylinder, a ball valve for controlling said passage, a ball positioning cage mounted on the end of said piston for rotary movement relative thereto, said cage and piston having cooperating abutment surfaces axially disposed from said end of the piston, said ball being freely displaceable through a predetermined distance between said piston and cage, a cylindrical spring positioned in said cylinder for engagement of its ends with said cage and said closed end respectively to transmit rotary movement from said cylinder to said cage and a piston stop in the wall of said cylinder for limiting the travel of said piston in said cylinder to prevent engagement of said cage and said cylinder.

3. In a hydraulic tappet, a cylinder provided with a closed end, a piston mounted for reciprocation in said cylinder, said piston having a central cavity formed therein and a passage providing communication between said cavity and the internal chamber formed by mounting said piston in said cylinder, a valve for controlling said passage, a valve positioning cage mounted on the end of said piston for rotary movement relative thereto, said cage and piston having cooperating abutment surfaces axially disposed from said end of the piston, said valve being disposed between said piston and cage with a predetermined clearance for freedom of movement axially of the passage, a cylindrical spring positioned in said cylinder for engagement of its ends with said cage and said closed end respectively, a piston stop in the wall of said cylinder for limiting the travel of said piston in said cylinder to prevent engagement of said cage with said cylinder and means for introducing a liquid to said cavity through the top of said piston.

4. In a hydraulic tappet a cylinder provided with a closed end, a piston mounted for reciprocation in said cylinder, said piston having a central cavity therein and a passage providing communication between said cavity and the internal chamber formed by mounting said piston in said cylinder, a valve for controlling said passage, a valve positioning cage mounted on the end of said piston for rotary movement relative thereto, said cage and piston having cooperating abutment surfaces a i lly disposed from said nd f the piston, said valve having a predetermined freedom of movement axially of the passage between said piston and cage, a cylindrical spring positioned in said cylinder for engagement of its ends with said cage and said closed end respectively, a piston stop in the wall of said cylinder to prevent engagement of said cage with said cylinder and means for introducing a liquid to said cavity through the side walls of said piston and cylinder.

5. In a hydraulic tappet actuating system, a cylinder provided with a closed end, means for simultaneously rotating and reciprocating said cylinder, a piston mounted in the cylinder for reciprocation and rotation relative thereto, said piston having a central cavity therein and a passage providing communication between said cavity and the internal chamber formed by mounting said piston in said cylinder, means for restraining rotary movement of said piston, a valve for controlling said passage, a valve positioning cage mounted on the end of said piston for rotation relative thereto, said cage and piston having cooperating abutment surfaces axially disposed from said end of the piston, said valve having a predetermined free operating clearance between said cage and the adjacent end of said passage, a cylindrical spring positioned in said cylinder for engagement of its ends with said cage and said closed end respectively to transmit rotary movement from said closed end to said cage and a piston stop in the Wall of said cylinder to prevent engagement of said cage with said cylinder.

6. In a hydraulic tappet, a cylinder closed at one end, a piston slidably fitted in the cylinder for axial rotation and reciprocation relative thereto, a body of thrust transmitting fluid between the piston and the closed end of the cylinder, said piston having a passage for supplying fluid to said body, a free valve movable in directions outwardly of the cylinder to close said passage and inwardly of the cylinder to open said passage, a valve retainer in abutment with the piston and rotatable relative thereto with the cylinder, said retainer havin a portion spaced from the piston within said fluid body and limiting the valve opening movement to a predetermined distance, said retainer and piston having cooperating abutment surfaces axially disposed from said end of the piston, and a spring drivably coupling the retainer and cylinder for concurrent rotation and urging the piston outwardly of the cylinder.

7. In a hydraulic tappet, a generally cup-shaped cylinder adapted for axial rotation and reciprocation in operation, a piston slidably fitted in the cylinder for rotation and reciprocation relative thereto, said piston having a passage extending through its end inwardly of the cylinder for supplying fluid to the closed end of the cylinder, said piston end terminating in a reduced diameter portion formed with a valve seat surrounding said passage, a valve engageable with said seat to close said passage, said valve being freely movable into and out of engagement with said seat in response piston and wear of said abutment surfaces serves to compensate for wear between said valve, valve seat and cage.

8. The invention defined in claim 3, wherein the piston is provided on its outer peripheral surface with a groove in communication with said cavity for returning liquid leaking between the piston and cylinder from said chamber in operation.

WILLIAM J. PURCHAS, J 3. ROBERT C. MOSER.

References Cited in the file of this patent Number UNITED STATES PATENTS Name Date Curran Feb. 23, 1915 Burleson Apr. 5, 1927 McAllister Apr. 12, 1927 George July 17, 1934 Daisley May 10, 1938 Eshbaugh June 11, 1940 Voorhies Apr. 8, 1941 Bergmann Mar. 30, 1948 

